CODEWITHSUNDEEP
bash
Nathan Smith
Nathan Smith

Reputation: 681

Should I evaluate a range?

Re-asking this here, since it doesn't belong in the Code Review SE.

I was always taught to never have static expressions in code, as it is an unnecessary operation that will always have the same output. For example, you would never have if 6 < 7 (aside from people slapping the occasional while true around).

That being said, I have a functioning bash script as follows:

#!/usr/bin/env bash
for i in {0..9}
do
    ...some stuff...
done

However, PyCharm is giving my hell for this re-iterating my concern in my first paragraph. It's counter suggestion is to have:

#!/usr/bin/env bash
for i in 0 1 2 3 4 5 6 7 8 9
do
    ...some stuff...
done

The logic is that it will not have to evaluate the range itself, thus increasing speed.

My Question

I think that the range looks nicer and, as far as I know, it won't actually affect speed (I don't mean noticeably, I mean at all), as it is simply iterating as it goes. Am I incorrect in thinking so?

It's a peeve of mine to waste cycles, but it's a greater peeve of mine to write grotesque looking code.

Upvotes: 0

Views: 43

Answers (1)

Charles Duffy
Charles Duffy

Reputation: 295580

The best practice approach in bash or other shells adopting ksh extensions is a C-style for loop:

for ((i=0; i<=9; i++)); do
  echo "Doing some stuff with $i"
done

This has advantages over the {0..9} syntax in that it works with variables ({$min..$max} doesn't work, because brace expansions happens before variable expansions do) and avoids needing to store the full list in memory at once, and it has advantages over 0 1 2 3 4 5 6 7 8 9 because the latter is hard to check for typos (it's trickier to visually spot the problems with 0 1 2 3 5 4 6 7 8 9 or 0 1 2 3 4 6 7 8 9).

Upvotes: 1

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